It is known that one of the main causes of transmission loss along a long distance optical link arises from noncoincidence of the axes of two optical fibers which are connected to each other, e.g. by welding. This requirement of excellent co-incidence of the fiber axes, which is already of great importance for multimode optical fibers, becomes essential for monomode optical fibers which have a considerably smaller core diameter, of about 10 microns.
Initially, optical fiber connection was performed using micrometer displacement devices using slides driven by very fine pitch control screws, said slides being crossed or superposed in a manner suitable for enabling displacements in any direction in three dimensions. However, it was quickly observed that the backlash existing in such slides does not make it possible to obtain accuracies of about one tenth of a micrometer as required, in particular, for connecting monomode optical fibers.
Attempts have therefore been made to replace slide devices by displacement devices that make use of deformable solids.
A device is described, in particular by the document FR-A No. 2 548 390, whose deformable solid is a centilevered beam operating by bending under the action of piezoelectric struts in two orthogonal planes. This beam comprises a succession of perpendicular hollows disposed along its axis and forming thin blades. This succession of hollows along the axis of a cantilevered beam gives rise to unwanted angular displacements of the end of the optical fiber which hinder proper alignment of said optical fiber with the optical component to which it is to be connected.
Preferred embodiments of the present invention provide a device for displacing the end of an optical fiber with better accuracy, and in particular a device which avoids unwanted rotation of the end of the optical fiber, and this is achieved by replacing the deformable solid constituted by a thin blade beam which is cantilevered and which operates in bending, by a deformable solid whose thin blades are disposed in a box shape with the cross-section of said box being perpendicular to the planes of the thin blades and to the axis of the optical fiber.
The document GB No. 2 080 471 describes a micromanipulator using pairs of thin blades acting as springs and disposed along the faces of a box shape, with the edges of the box being constituted by prismatic blocks in which the ends of the thin blades are fixed.
The accuracy of the displacements obtained with such a device is not sufficient. It is very difficult to fix thin blades to prismatic angle blocks without any angular or longitudinal backlash. In addition, the blades are of constant cross-section such that the bending stress varies along a blade. Its value is at a maximum in the immediate vicinity of the angle blocks. Also, some of the substance in the middle regions of the blades is not only useless, but is also harmful, since it reduces the deformation of the blade when subjected to a given force.
The deformable solid of the present invention is made as a single part in order to avoid any geometrical defects due to assembling a plurality of distinct parts and to avoid any possibility of movement of one part relative to another. In addition, the blades of this deformable solid are of reduced thickness in their middle regions, with the variation in thickness from one end to the middle region being such that the stress in the material is substantially the same in any right cross-section of the blade.